Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV) and hybrid electric vehicles (HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuel.
Small-sized mobile devices use one or several battery cells for each device. On the other hand, middle- or large-sized devices, such as vehicles, use a middle- or large-sized battery system having a plurality of battery cells electrically connected with each other because high output and large capacity are necessary for the middle- or large-sized devices.
The middle- or large-sized battery system, which is used as a charging and discharging power source for electric vehicles and hybrid electric vehicles, is manufactured by electrically connecting a plurality of battery modules (battery cells) in series/parallel with each other and mechanically coupling the battery modules (battery cells) to each other.
Generally, a slave battery management system (BMS) is mounted to each battery module, and a master BMS is mounted to each battery module assembly, which includes a plurality of battery modules, for controlling the charge and discharge of each battery module and performing a control operation necessary to secure the safety of each battery module during the abnormal operation of each battery module. For securing the safety of each battery module and each battery module assembly, a control unit includes a control circuit for interrupting the operation of an abnormally operated battery module(s) or an abnormally operated battery module assembly(ies).
A large amount of energy is stored in each battery module after each battery module is charged. When each battery module is abnormally operated in this state, however, the charged energy assists in the abnormal negative reaction of each battery module, while each battery module is not connected to a corresponding external input and output terminal, with the result that the battery module may reach a dangerous state. For example, when a specific battery module is abnormally operated, during the movement of an electric vehicle, the dangerous state is maintained or further accelerated during the movement of the vehicle, if the abnormally operated battery module is not immediately replaced with a new one, even though a connection circuit for the abnormally operated battery module is broken.
Consequently, there is a high necessity for a technology that is capable of fundamentally solving the several above-mentioned problems.